Motion picture photographic films that are used as print films for movie theater projection have long used a carbon black-containing layer on the backside of the film. This backside layer provides both antihalation protection and antistatic properties. The carbon black is applied in an alkali-soluble binder that allows the layer to be removed by a process that involves soaking the film in alkali solution, scrubbing the backside layer, and rinsing with water. This carbon black removal process, which takes place prior to image development, is both tedious and environmentally undesirable since large quantities of water are utilized in this film processing step. In addition, in order to facilitate removal during film processing, the carbon black-containing layer is not highly adherent to the photographic film support and may dislodge during various film manufacturing operations such as film slitting and film perforating. Carbon black debris generated during these operations may become lodged on the photographic emulsion and cause image defects during subsequent exposure and film processing.
After removal of the carbon black-containing layer the film's antistatic properties are lost. Undesired static charge build-up can then occur on processed motion picture print film when transported through projectors or on rewind equipment. Although these high static charges can discharge they cannot cause static marks on the processed photographic film. However, the high static charges can attract dirt particles to the film surface. Once on the film surface, these dirt particles can create abrasion or scratches or, if sufficiently large, the dirt particles may be seen on the projected film image.
In U.S. Pat. No. 5,679,505 herein incorporated by reference, a motion picture print film is described which contains on the backside of the support, an antistatic layer and a protective topcoat. The protective topcoat is comprised of a polyurethane binder and a lubricant. The polyurethane binder has a tensile elongation to break at least 50% and a Young's modulus measured at 2% elongation of at least 50000 lb/in.sup.2.
However, post processing tar deposits and stain have been a problem with protective overcoats in motion picture print film. This tar is derived mostly from polymeric oxidized developer. The problem with most polyurethane protective overcoats is that invariably such polymers are inhomogeneous compositionally and this coupled with the fact most polyurethanes have hard and soft segments, domain structures are imparted to their coated surfaces. This can greatly increase the chances of deposition or adsorption of foreign matter to the surface.
The present invention relates to eliminating tar pickup during processing by providing a continuous polyolefin based hydrophobic overcoat that is derived from an aqueous medium resulting in a chemically homogeneous low surface energy coating resistant to tar adsorption.
Further, having the non-water permeable polyolefin overcoat of this invention, ensures protection of the underlying antistat layer from processing solutions. The low coefficient of friction that the polyolefin provides eliminates the need for an added lubricant in the top coat.